The U.S. Navy heard the likely implosion of the missing Titan sub on Sunday

Sensors operated by the Navy detected the likely implosion of the Titan submersible hours before the U.S. Coast Guard publicly shared that it had gone missing — a revelation that means a five-day search that sparked round-the-clock media coverage may have been futile from the start.

The Navy detected "an anomaly consistent with an implosion or explosion" in acoustic data taken from the same area where the Titan went missing, a senior Navy official told NPR in a written statement.

A second official confirmed to NPR that it had registered that acoustic data on Sunday.

"While not definitive, this information was immediately shared with the Incident Commander to assist with the ongoing search and rescue mission," the first official said. "The decision was made to continue our mission as a search and rescue and make every effort to save the lives on board."

It was midday Monday that the Coast Guard first tweeted that it was searching for the Titan. The 22-foot-long, Titanic-touring vessel was carrying four tourists and a pilot when it lost communication with its control ship less than two hours into its dive on Sunday, roughly 900 miles off the coast of Cape Cod.

The massive search operation involved international ships, surveillance aircraft and undersea drones. Officials and experts from the unified command consistently told reporters that the Titan's passengers may be subsisting on emergency oxygen supplies.

When asked as late as Thursday morning whether he had hope for rescuing the sub's passengers, U.S. Coast Guard Rear Adm. John Mauger said that "people's will to survive" must be considered in complex search operations.

The world watched along in fascination until a remote-operated vehicle found the sub's tail cone and other debris on the seafloor, approximately 1,600 feet from the Titanic's bow. All five of the people aboard the vessel were declared dead.

The Coast Guard confirmed to NPR it was aware of the data as part of the unified search command.

OceanGate, the private company behind the sub, was also part of the unified command. In response to NPR's request for confirmation that OceanGate knew of the Navy's acoustic data, spokesperson Andrew Von Kerens responded by saying the company had "no additional information to share."

The listening system the Navy used to register the noise is believed to be the Sound Surveillance System or SOSUS, according to information shared with NPR by a senior Navy official. SOSUS, an underwater cable system that has been in place for decades, is capable of detecting underwater anomalies that might indicate the presence of foreign submarines.

The Wall Street Journal first broke the news of the data on Thursday, prompting some in the deep sea community to disclose that they also knew of the implosion indicator early on.

James Cameron, director of the 1997 blockbuster film Titanic, told CNN's Anderson Cooper that he called some of his diving connections and "tracked down some intel that was probably of military origin" to confirm his hunch of an implosion on Monday.

"Then I watched over the ensuing days this whole, everyone-running-around-with-their-hair-on-fire search," he said. "I just feel terrible for the families that had to go through all these false hopes that kept getting dangled as it played out."

The exact cause of the implosion is still unknown, and the unified search command said it would continue scanning the site where it uncovered the Titan debris.

The safety record of OceanGate, and the Titan's ability to withstand the pressure at depths of more than 12,000 feet, had both been called into question in recent days. Industry experts, former employees and previous passengers had all raised concerns, especially about the experimental design of the hull.

Oceanographer Bob Ballard, who has conducted over 150 deep-sea expeditions, said that the public may not "appreciate the amazing energy" behind an undersea implosion.

Ballard told ABC News on Thursday that "it literally shreds everything. It's extremely powerful."

NPR's Tom Bowman contributed reporting. [Copyright 2023 NPR]